Image forming apparatuses, such as copiers, facsimiles, and printers, which form toner images on recording media, are widely used. In such an image forming apparatus, toner is heated and softened to be fixed on a recording medium. To reliably fix the toner on the recording medium, the toner is required to soften sufficiently. Because the toner needs a large amount of heat to sufficiently soften, a large amount of electric power is consumed, which runs counter to recent trends toward greater energy conservation. The proportion of electric power consumed during fixing toner on recording media to total electric power consumed by an image forming apparatus is relatively high. Therefore, it is desirable that electric power consumption be reduced as much as possible. Accordingly, there have been various attempts to reliably fix toner on recording media using less power.
For example, Japanese Patent No. 4224076 (JP-4224076-B) proposes applying a fixing liquid to a toner image on a recording medium to soften and/or swell toner. Such a technique meets energy conservation because no heat is required. In addition, JP-4354164-B also proposes a technique requiring no heating which applies a fixing liquid to a toner image on an intermediate transfer member so that the toner image is transformed into an adhesive film and the film-shaped toner image is fixed on a recording medium by its adhesiveness.
However, for the above-described techniques, the toner image may be disturbed upon application of the fixing liquid. To cope with such a challenge, as disclosed in JP-4224076-B, the fixing liquid is applied to toner images on a recording medium by a non-contact ink jet method. The application amount of the fixing liquid is gradually increased along the direction of feed of the recording medium. However, the toner powder tend to scatter and contaminate nozzles of the ink jet head upon reception of the ejected fixing liquid even when the application amount of the fixing liquid is small. As a result, the nozzles may be clogged with the toner powder. Moreover, in order to reliably fix a toner image on a recording medium, a relatively large amount of the fixing liquid is needed so that the fixing liquid reliably reaches the contact point of the toner image and the recording medium. However, when such a large amount of the fixing liquid is applied, a large amount of heat is needed for drying, resulting in undesired increase in energy consumption and drying time.
In JP-4354164-B, as described above, a toner image on an intermediate transfer member is transformed into a toner film upon application of the fixing liquid at environmental temperatures. With such a technique, the fixing liquid may contaminate image forming parts and undesirably form a toner film on the image forming parts at environmental temperatures. In addition, because the fixing liquid transforms toner into a toner film at environmental temperatures at which the image forming apparatus is used, the fixing liquid may adversely affect other components in the apparatus.
JP-2007-121652-A describes an image forming apparatus employing a wet developing method using a liquid developer comprising a toner and a carrier liquid. In this image forming apparatus, a fixing liquid, which is compatible with the carrier liquid, is previously applied to a recording medium and a toner layer is formed on the recording medium by the wet developing method. The carrier liquid existing between the toner particles in the toner layer is flowed so that the toner layer is dissolved and swelled to be fixed on the recording medium. This technique can prevent image disturbance upon application of the fixing liquid, but may cause image disturbance upon interaction between the fixing liquid and the carrier liquid. In addition, because the fixing liquid works at environmental temperatures at which the image forming apparatus is used, the fixing liquid may adversely affect other components in the apparatus. In addition, the technique can result in a delay when the fixing liquid is applied before an image is transferred onto the recording medium compared to when the fixing liquid is applied after the image is transferred onto the recording medium. Further, the fixing liquid compatible with the liquid developer may not be applicable to other images formed without the liquid developer.
As a result, image recording methods which eject toner onto a recording medium, such as toner jet, direct toning, and toner projection, have been proposed in, for example, JP-2009-39977-A. In these methods, a liquid is applied to a recording medium before a toner image is formed thereon. Therefore, image disturbance due to application of liquid can be prevented. However, it requires a large amount of heat to dry the liquid, resulting in high electric power consumption and an extended fixing time. The liquid applied to the recording medium includes a softener that dissolves or swells resins included in toner. Thus, the recording medium to which the liquid is applied prevents toner from scattering and accelerates fixation of the toner. Specifically, the liquid is absorbed by fibers of the recording medium. Such fibers absorbing the liquid are soft enough to prevent toner from scattering. To further dissolve or swell the toner to accelerate toner fixation, the liquid needs to reliably contact the toner. This is because the recording medium to which the liquid is applied has a higher adhesive force to toner and a lower repulsive force to toner. When the ejected toner reaches and adheres to the recording medium, only a slight amount of the liquid existing at the surface of the recording medium can contact the toner and most of the liquid cannot penetrate the toner layer. In this case, the toner may scatter and may not be reliably fixed on the recording medium. In a case in which the liquid is previously applied to an intermediate transfer member before a toner image is formed thereon, penetration of the liquid into the toner image may be accelerated. However, the liquid may adversely affect image forming members.
JP-2007-301818-A proposes a technique with a mechanism of sealing a treatment liquid for enhancing image quality and robustness onto a recording medium. Such a configuration minimizes evaporation of the moisture of the treatment liquid to maintain the function of the treatment liquid and also prevents adherence of the treatment liquid to other members otherwise caused by scattering of the liquid.
However, such liquids capable of enhancing fixing performance to reduce electric power consumption in fixing may cause, for example, image disturbance, increase in electric power consumption for drying, lengthening of fixing duration time, contamination of image forming members, and reduced performance of the liquid. An art capable of preventing such failures and applicable to a method other than liquid development has still not been proposed.